求dalao优化

#include<bits/stdc++.h>
using namespace std;
int bx,by,dx[2]={1,0},dy[2]={0,1};//卒 
int mx,my,mx10[8]={-2,-1,1,2,2,1,-1,-2},my10[8]={1,2,2,1,-1,-2,-2,-1};//马 
int vis[25][25];
long long ans;
void dfs(int x,int y){
	if(x==bx&&y==by){
		ans++;
		//cout<<ans<<" ";
		return;
	}
	for(int i=0;i<2;i++){
		int px=x+dx[i],py=y+dy[i];
		if(px>=0&&px<=bx&&py>=0&&py<=by&&!vis[px][py]){
			vis[px][py]=1;
			dfs(px,py);
			vis[px][py]=0;
		}
	}
	return;
}
int main(){
	cin>>bx>>by>>mx>>my;
	vis[mx][my]=1;
	for(int i=0;i<8;i++){
		vis[mx10[i]+mx][my10[i]+my]=1;
	}
	vis[0][0]=1;
	dfs(0,0);
	cout<<ans;
	return 0;
}